Residual Oil Zones:

In the course of historical oil field development, the Oil/Water Contact (OWC) formed the base level of drilling. When water production became dominant, the best approach was to terminate drilling at the OWC. Recent work in the Permian Basin has shown that commercial recovery of oil can be found beneath the OWC in what we have come to refer to as Residual Oil Zones (ROZs). These ROZs can be ubiquitous and quite thick. In particular, the Wasson and Seminole fields have as much as 300 feet in the interval with OOIP numbers rivaling the main pay zone. The oil recovery concept can be most simply described as using CO2 injection, as in a pattern-type CO2 flood, to recover oil from zones that may possess water saturations as high as 75% of the pore space. The concept is analogous to CO2flooding water swept intervals in the main pay where water saturations have risen to 50-75% due to the waterflood. For more information click: Stranded Oil in the Residual Oil Zone.

General ROZ Research

As EOR projects are expanded to reservoirs below the oil/water contact (brownfields) or to areas with only residual oil targets (greenfields), some interesting experience is developing. What we are seeing is that the reservoirs in the Permian Basin’s San Andres formation dolomites are (1) more pervasively dolomitized, more so than the Main Pay Zones (MPZs), (2) have a very live oil in the upper 100 feet of the ROZ, (3) appear to nominally process faster than the MPZs, and (4) appear to have decaying lighter end components with depth, i.e., and a working hypothesis that the lighter components in oil within the vertical ROZ intervals often decay with depth. We hypothesize that the latter observation is either due to the original paleo trap, density stratification, or is induced from effects of the paleo waterflood. Also, we are still trying to better forecast why certain projects witness injectivity losses after Water – Alternating – Gas (WAG) cycles, while some do not. We are beginning to see a correlation of greater injectivity losses with greater oil wetting which appears to be more common in the ROZs. ROZ flooding is still immature and some of us are worried that the long proven WAG approaches and strategies for the MPZs are not going to work as well in mature ROZ floods.

A ROZ Research Group has been formed under our local non-profit organization, the Applied Petroleum Technology Academy (www.aptapb.org), and liaisons have been developed to further understandthe above and other research questions: Enhanced Oil Recovery Institute of the University of Wyoming http://www.uwyo.edu/eori (medium gravity oils in ROZs and wettability), University of North Dakota’s Energy and Environmental Research Centerhttp://www.undeerc.org (CO2 dense phase behavior and lab testing), The University of Texas of the Permian Basin http://ceed.utpb.edu (mapping of ROZ spatial distributions and log analyses), Advanced Resources International http://www.adv-res.com (computation modeling), and Stanford University (core flooding, two- and three-phase CO2 behavior).

ROZ Fairway Research

Residual Oil Zones do not just appear below main pay zones; some of the largest lie in areas beyond where no MPZs are present. Mapping the fairways of occurrence in the Permian Basin is underway in a current project (seeresidualoilzones.com).

Melzer Consulting is very actively involved in researching the residual oil zones (ROZs) both in the Permian Basin and elsewhere. In their U.S. Department of Energy report, Steve Melzer documented the three types of ROZs we have found as we study reservoirs throughout the world. Type 3 (laterally flushed) ROZs (Type 3 video below) appear to be the most common type and the ones currently being commercially exploited (all within the San Andres formation in the Permian Basin). However, the other two types shown in the videos(Type 1 video below; Type 2 video below) are also common. Work is continuing on document the origins and distribution of the ROZs as well as flood response as in the Goldsmith field in Ector County, Tx.